The present invention relates to an improved method and apparatus for dispensing fluids under pressure. More particularly the present invention is directed to the dispensing of liquids under pressure by means of an expandable resilient bladder.
A large variety of different types of apparatus is available for dispensing fluids, particularly liquids, from handheld bottles, cans and other containers. Such apparatus includes squeeze bottles, pressure packs, aspirators, and various sorts of mechanical pumps, ranging from the very simple to the very sophisticated.
For a number of years now one of the most popular and widely used forms of dispensers has been the pressure pack, particularly the so-called aerosol dispenser. The aerosol dispensers have been particularly popular for dispensing hair care products and personal hygiene products. The major advantage of the aerosol type dispenser is that it develops sufficient pressure on the fluid to be dispensed to provide the quantity of energy needed for atomization of the liquid. Thus, it is well known that the finer the droplet size required in a spray, the greater is the quantity of energy which must be supplied.
However, aerosol products presently known have come under scrutiny as possible health hazards when used for certain products. Thus, the propellants generally used may be hazardous when inhaled. Moreover, the potential pressures developed in some aerosol containers and products may also create safety hazards because of the possibility of explosions.
A recently developing alternative to the use of aerosol propellants for providing the motive force in pressure pack dispensers has been the development of resilient elastomeric bladders or sacks within the container or dispenser for the fluid. The resilient or elastic properties of the bladder provide the physical pressure on the fluid for dispensing as a pressurized product.
Although such elastomeric bladders have been around for many years in various crude and simple forms, two major problems have attended the use of such apparatus. First of all, it has been extremely difficult or impossible to obtain the relatively high pressures which may be obtained with the use of aerosol propellants. Secondly, a significant portion of the fluid product is usually wasted due to the fact that the pressure exerted by the bladder expires well before the bladder is completely empty, and there is no way of utilizing the remaining product in the bladder.
In recent years, the latter disadvantage has been greatly reduced by resorting to various means of pre-stressing or pre-tensioning of the bladder. That is, during the manufacture of the dispenser, some means is provided for stretching or tensioning the bladder prior to the filling of the dispenser with the fluid. Examples of such pre-tensioning devices are disclosed in U.S. Pat. Nos. 3,738,538; 3,506,005; 3,698,595; 3,361,303; 3,672,543; 3,767,078; 3,468,308 and 3,469,578.
Unfortunately, the aboe pre-tensioning device have not completely solved the problem of expelling substantially all of the fluid from the bladder. Moreover, even with the use of pre-tensioning, the pressure on the fluid has been found to decrease rather steadily as the bladder is emptied, so that uniform pressure is not provided for dispensing the product. Since proper atomization requires pressure and energy, the reduction in pressure may result in a good, fine spray when the dispenser is full, but a poor, drippy spray when the dispenser is almost empty.
Accordingly, it is desirable to have a non-aerosol type pressure pack dispenser which will not only be capable of dispensing substantially all of the fluid product contained therein, but will also provide a substantially uniform pressure throughout the dispensing of the fluid.